The e-mails, which date from July 2004 to December 2011, "reveal the inner workings" of Strategic Forecasting (Strafor), an Austin, Texas-based that provides security analysis to the U.S. Army, Lockheed Martin, and Northrop Grumman, the embattled document-sharing site said in a statement.
"The emails show Stratfor's web of informers, pay-off structure, payment-laundering techniques, and psychological methods," the organization said.
The trove also purportedly contains more than 4,000 e-mails mentioning WikiLeaks or its founder, Julian Assange.
"Here we have a private intelligence firm, relying on informants from the US government, foreign intelligence agencies with questionable reputations, and journalists," Assange told Reuters. "What is of grave concern is that the targets of this scrutiny are, among others, activist organizations fighting for a just cause."
The source of the e-mails was not revealed, but Stratfor disclosed in December that its Web site had been hacked and information about its corporate subscribers was compromised. AntiSec, an Anonymous-affiliated hacktivist group, quickly claimed responsibility and promised "mayhem" with plans to release even more documents.
Strafor founder George Friedman said in January that the attack was "clearly designed to silence us by destroying our records and the Web site" but that no classified data was obtained during the hack.
WikiLeaks and Assange incurred the wrath of the U.S. government in 2010 by posting online a vast repository of classified and sensitive documents from military and diplomatic sources. A U.S. soldier, Bradley Manning, has been charged with supplying a large portion of that haul to Assange and WikiLeaks. If Manning is eventually found guilty, he could face life in prison.
Separately, Assange, who has been living in the U.K. under bail, is awaiting extradition to Sweden on charges that he sexually assaulted two women in 2010, charges that he has vehemently denied.